1. Field of the invention
The present invention relates to a device for producing a leno selvedge for a loom with heald frames according to the preamble of claims 1 and 2.
2. Description of the prior art.
JP-369 627 discloses a planet rotator for producing a leno selvedge. This is a device in which the planet wheels carry the bobbins, which means that the bobbins are also rotating. The device works in such a manner so that the planet wheels are guided according to the angle of rotation of the heald frames. That means that such a planet rotator for producing a leno selvedge executes a continuous motion of rotation corresponding to the motion of the angle of rotation of the heald frames, that is that a mating angle of rotation of the heald frames is associated to each angle of rotation of the planet rotator.
Indeed, such a planet rotator is working irrespective of the drive of the heald frames, which makes it possible to have the planet rotator leading or lagging behind the heald frames with regard to the angle of rotation.
A device for producing a leno selvedge is known for example out of DE 44 05 776 C 1. There, an electrically driven motor operator is provided, which actuates a doup disc, whereby the doup disc constitutes the rotor of the electrically driven motor operator. The doup disc itself has at least two guide elements for the doup ends, whereby the leno selvedge is formed by turning the doup ends around the weft thread.
The WO 97/24479 discloses a device for producing a leno selvedge, whereby the rotor of an electric motor is provided with arms for guiding the doup ends. Here too, the leno selvedge is produced by wounding the doup ends guided by the arms around the weft thread.
These two well-known devices have in common that, to produce the leno selvedge, an electric motor is provided that at any time synchronizes with the motion of the heald frames. However, this electric motor can also be actuated so that it is dephased relative to the motion of the heald frames, in order for example to allow an early tying of the weft thread. But actually, an orientation of the motion of the electric motor's rotor always occurs relative to the motion of the frame. This clearly shows that, in order to execute this described synchronization of the leno selvedge device with the motion of the heald frames, data continuously have to be transmitted, in particular from the drive shaft of the loom to the leno selvedge device, so that the synchronization of the electric motor of the leno selvedge device with the loom, that is with the motion of the heald frames, can be achieved. In this respect it has also been foreseen that the electric motor is coupled to the actuation of the loom via a so-called electric shaft. This does not mean that, in the known device, the control of the leno selvedge device is depending on the heald frame; on the contrary, the control and, accordingly, the motion of rotation of the electric motor's rotor of the leno selvedge device does not depend on the heald frame, since no direct mechanical coupling is provided between the heald frames and the leno selvedge device. Still, as already explained, the leno selvedge device is coupled with the loom in as much as the motion of the leno selvedge device, that is of the electric motor's rotor, is synchronized with the motion of the drive shaft of the loom, or according to the motion of the heald frames.
It however proved to come to the same whether, for producing a leno selvedge, the rotor of the electric motor of the leno selvedge device is or not exactly and at any time synchronized with the motion of the loom--that is of the drive shaft or the heald frames of the loom respectively. The only essential point is rather that, when the leno selvedge device is starting the weft insertion, the two doup ends are also in the open position of the shed and that, once the weft insertion has been accomplished, the doup ends are going into their closed position of the shed. That means that the essential point is exclusively that the respective final position, i.e. "open shed" or "closed shed" is reached by the leno selvedge device at the latest when the heald frames are occupying an appropriate position. The consequence thereof is that a synchronization at all time of the motion of the electric motor's rotor with the motion of the heald frames is not at all necessary.